1. Field of the Invention
The present invention relates to a method of stacking ceramic green sheets, and more particularly, the invention relates to a method of stacking ceramic green sheets for manufacturing a multilayer ceramic electronic component.
2. Description of the Background Art
In order to manufacture a multilayer ceramic electronic component such as a :multilayer ceramic capacitor, for example, it is necessary to stack ceramic green sheets.
The thickness of such ceramic green sheets is advantageously minimized for attaining large electrostatic capacitance in, for example a multilayer ceramic capacitor. Thus, the distances between internal electrodes can be reduced and the number of layers of such internal electrodes can be increased in a prescribed dimensional range.
In order to stack such thin ceramic green sheets, a transfer technique is advantageously employed. According to this transfer technique, a ceramic green sheet is lined with a proper back film and compression-bonded in this state to other ceramic green sheets which are already stacked with each other so that the former ceramic green sheet is transferred to the stacked ceramic green sheets. Thereafter, the back film is separated from the transferred ceramic green sheet.
In order to obtain a multilayer ceramic capacitor through the aforementioned transfer technique, two methods are typically carried out as follows:
(1) A ceramic green sheet, which is formed on a back film, and internal electrode films, which are formed on another back film, are alternately transferred.
(2) As shown in FIG. 4, internal electrode films 2 are provided on a back film 1 and a ceramic green sheet 3 is formed on this back film 1 to cover the internal electrode films 2, so that the internal electrode films 2 and the ceramic green sheet 3 are integrally transferred. Alternatively, a ceramic green sheet 3 is formed on a back film 1 and internal electrode films 2 are provided on the ceramic green sheet 3 as shown in FIG. 5, so that the ceramic green sheet 3 and the internal electrode films 2 are integrally transferred.
However, the aforementioned method (1) has low productivity since the internal electrode films and the ceramic green sheet are alternately transferred, and hence this method has been applied only to specific items. On the other hand, the method (2) has excellent productivity since the internal electrode films 2 and the ceramic green sheet 3 are already integrated with each other which facilitate the handling.
In the transfer technique, discussed above transferability of the ceramic green sheets depends on the effective action of a binder contained in the ceramic green sheets, sufficient smoothness of the surface of the ceramic green sheet which is brought into contact with the already stacked ceramic green sheets to be transferred thereto, and the like.
However, as shown in FIG. 4 or 5, on the surface 4 of the ceramic green sheet 3, which is formed on the back film 1 ceramic particles are arranged randomly so that the sheet surface is irregular and has with insufficient smoothness. Thus, the adhesiveness provided by the surface 4 of the ceramic green sheet 3 is reduced thereby causing defective transfer of the ceramic green sheet 3. This problem also arises in the aforementioned method (1).
In the aforementioned method (2), however, the ceramic green sheet 3 is provided with the internal electrode films 2 on either surface, and hence such internal electrode films 2 are necessarily interposed between two ceramic green sheets which are brought into contact with each other in a transfer step. The adhesive strength between the ceramic green sheet 3 and the internal electrodes 2 is inferior to that the adhesive strength between the two ceramic green sheets. Thus, the aforementioned problem of a reduction in adhesive strength caused by drying of the surface 4 of the ceramic green sheet 3 is particularly serious in the aforementioned method (2).
As hereinabove described, in order to obtain a miniature multilayer ceramic capacitor having large capacitance it is necessary to reduce the thickness of the ceramic green sheets. In doing so, however, defects such as pinholes are increased so that the defective rate of the completed multilayer ceramic capacitors is increased.
The aforementioned problems arise not only in multilayer ceramic capacitors but in general multilayer ceramic electronic components which are manufactured through steps which include the step of stacking ceramic green sheets.